This invention relates to the electroless plating of non-metallic substrates such as polymeric substrates and more particularly to the plating of such substrates by the grafting of one or more polymerizable monomers, and polymerizing such monomers, to form a coating on the substrate surface in the presence of silver ions. Copper is then deposited on the grafted layer from an electroless plating solution with silver atoms held in the interstices of the polymerized coating acting as nucleating agents for the deposition of metallic copper.
The electroless plating of polymeric substrates by the seeding of the substrate with a precious metal such as palladium is known. The palladium seeding process however, is expensive, since the use of palladium adds substantially to the cost. It is also known to use silver ions to generally initiate polymer grafting on a substrate. Such processes generally are disclosed in U.S. Pat. Nos. 3,698,931 (Horowitz), 3,801,478 (Heger et al), and 3,847,649 (Sova).
While the methods disclosed in the above prior art patents may provide an acceptable bonding of a metal film to a polymeric substrate, the processes in some cases are still excessively expensive, since they require a substantial amount of silver. Further, the bond that is formed between the metal layer and the polymeric substrate may be subject to attack by water or may be thermally decomposable. In such prior art processes the use of excess silver salt adds substantially to the cost of the process. Further, the use of excess silver salt tends to make the metal film much more sensitive to attack by water, since the plating is subject to attack by water and eventual weakening of the film bond, because of the salt layer underlying the plated film.
Accordingly, it is an object of the present invention to provide a process for the electroless plating of a non-metallic substrate such as a polymeric substrate with silver ion used as an initiator for grafting one or more unsaturated monomers onto the substrate and then electrolessly plating a metal onto the silver atoms held in the interstices of the grafted polymerized coating on the substrate.